An outbreak (159 cases) of transient thyrotoxicosis without hyperthyroidism in Japan

Clinical characteristics and outcomes of an exogenous thyrotoxicosis epidemic in prison

Introduction

An outbreak of exogenous thyrotoxicosis is an uncommon cause of thyrotoxicosis. This study aimed to investigate the characteristics and outcomes of exogenous thyrotoxicosis and electrolyte imbalance in a prison during an outbreak of exogenous thyrotoxicosis in the Phitsanulok, Thailand prison.

Methods

This study collected cross-sectional data during an outbreak of thyrotoxicosis among inmates at Phitsanulok prison between 29 December 2019 and 17 January 2020. In the first phase, a total of 2815 prisoners were screened for thyroid-stimulating hormone (TSH), potassium levels and pulse rate. In the second phase, samples from 490 male prisoners were collected for test on thyroid function, serum electrolytes and urine electrolytes. Thyroglobulin levels were also measured in patients with thyrotoxicosis. A questionnaire was used to obtain patient information about signs and symptoms of thyrotoxicosis.

Results

The prevalence of subclinical thyrotoxicosis was 78.1%. The pulse rate was significantly higher in the subclinical thyrotoxicosis group. Weight loss, palpitation, muscle weakness and fatigue were found predominantly in the subclinical thyrotoxicosis group. The prevalence of hypokalaemia was 38.4%; however, there was no difference between subclinical thyrotoxicosis and normal TSH. The mean magnesium levels were significantly lower in the subclinical thyrotoxicosis group. Patients with hypokalaemia mainly showed potassium loss through the kidneys. Almost all patients with suppressed TSH levels had low to normal thyroglobulin levels. In addition, the mean of calculated total step-up deiodinase activity in patients with subclinical thyrotoxicosis was lower than 30 nmol/s, which was an additional clue to confirm exogenous thyrotoxicosis. The frozen meat during the outbreak had higher levels of thyroid hormone compared with the control group.

Conclusions

With an outbreak of thyrotoxicosis, most likely due to exposure to exogenous thyroid hormone in frozen meat, our findings have raised awareness of nutritional problems in prison. The development of surveillance systems to prevent outbreaks is urgently needed.

Familial occurrence of silent thyroiditis

Two brothers and their mother, who had allergic rhinitis caused by Japanese cedar pollen, developed silent thyroiditis in spring. In addition, these three patients had the same HLA haplotype. Another brother, the father, and the paternal grandmother, who did not have allergic rhinitis caused by Japanese cedar pollen, did not show symptoms of silent thyroiditis. The present study indicates that genetic and/or environmental factors are important in the development of this familial type of silent thyroiditis.